AMCI SD4840EK, Руководство пользователя

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79
TASK 1
M
OTOR AND
P
OWER
S
UPPLY
S
IZING
1.1 Sizing Your Motor
Your motor choice is based on the output torque you need, the mounting space you have, and your budgetary
constraints. Torque curves for all of the motors available from AMCI are presented on the following pages.
Torque curves show the performance of the motors at the specified current.
There are a few things to remember when choosing your motor based on torque curves.
1) The torque curves in this manual are for the SD4840EK. You cannot use these curves to accurately
determine the amount of torque from an AMCI motor when it is attached to a different drive. Nor can you
accurately determine the amount of torque from a motor when attached to an SD4840EK if its torque
curves were generated using a different drive. In general, if an output bus of the foreign drive is not the
same as the voltage supplied to the SD4840EK, then the torque curves will be less accurate at higher
speeds.
2) Make sure that the motor can provide the needed torque over the entire speed range of your application.
Available torque drops as speed increases, so evaluate the motor’s torque at its highest operating speed.
3) All of the torque curves show when the motor’s windings are attached to the SD4840EK in parallel.
Parallel attached motors have the advantage of more torque at high speeds when compared to series
attached motors.
A simple guideline is to use the largest motor your mounting space and budgetary constraints allow. Because
the I
2
R losses in the motor’s windings manifest themselves as heat, the maximum allowable motor tempera-
ture limits the motor’s current. Using the largest motor possible may allow you to use a lower current setting
on the SD4840EK drive. This lowers the I
2
R losses, and the operating temperature of the motor, which
increases the motor’s life.
1.2 Determining Your Motor Current Setting
Your motor current setting is based on the amount of torque needed from the motor. If you decide to use a lower
current setting than the value listed in the curve, be aware that a reduction in current proportionally reduces the
holding torque. However, a reduction in current may not lead to a proportionally reduction in torque at high
speeds, especially if the motor is series connected. At high speeds, motor torque is limited by the voltage bus of
the drive and the inductance of the motor. (The simplest explanation is that the drive does not have enough time
to establish the full current through the motor before it must switch the current to the winding.)
Because of this, its difficult to calculate the exact amount of high speed torque a motor will give you when
you reduce its current setting. Its often easier to determine your optimum current setting by testing your
machine at various current settings and then deciding which setting gives you the best performance.
1.2.1 A Note on Microstepping
Many microstepping drives control the peak current through the motor. At low speeds, this type of current
control drops the available torque of a micro-stepped motor to approximately 70.7% of that available when
the motor is full stepped.
However, the SD4840EK controls the RMS current through the motor. Therefore, the current supplied by the
SD4840EK when microstepping is always the power equivalent of the full step current. This means that the
motors’ full torque is always available. At very low speeds, the SD4840EK automatically switches to peak
current control to prevent motor damage.
This section is intended for anyone that need performance data on compatible
AMCI stepper motors or guidelines for using a foreign stepper motor.